Underground transformer unit



1935- J. s. PARSONS UNDERGROUND TRANSFORMER UNIT Filed June 21, 1933 INVENTOR 70/7 5. Par-5005.

WITNESS ES:

ATT ORNEY Patented Dec. 17, 1935 UNITED STATES 2,024,742 UNDERGROUND TRANSFORMER UNIT John S. Parsons, Swissvale, Pa., assignor to Westhouse Electric & Manufacturing Company,

East Pittsburgh, sylvania Pa., a corporation of Penn- Application June 21, 1933, Serial No. 676,852

4 Claims.

My invention relates to electrical distribution apparatus and particularly to transformersand associated switchgear apparatus for use in underground distribution systems.

In such systems it is the practice to provide brick, concrete or masonry vaults for housing the distribution transformers and associated apparatus. The vaults are commonly located under streets and sidewalks or in other available locations, in some cases being parts of buildings used for other purposes. As underground distribution is used principally in densely settled and metropolitan areas, the underground locations where it is desired to install transformer vaults are often occupied by other subsurface structures, such as pipes of various kinds, drains, communication cables, etc. As masonry materials are very poor conductors of heat it is necessary to make the vaults of capacious construction in order to properly dissipate the transformer heat losses, and the location of such cumbersome becomes valueless.-

In order to avoid the above-mentioned difficulties of vault construction, attempts have been made to bury the transformer directly in the ground without the protective vault. Such attempts have, in general, been unsuccessful, because the heat generated in the transformer tends to bake the soil in its immediate vicinity into a dry, heat insulating layer. This results in excessive temperature rise in the transformer, excessive losses and such poor efliciency as to ex clude the arrangement commercially.

In accordance with my invention, I provide a buried transformer unit havingan outer casing of good heat conducting material such as sheet steel, separated from an inner casing or tank by an air space which communicates with the atmosphere. I provide means for circulating air from the atmosphere through this space in sufficient quantity to prevent baking of the soil adjacent the outer casing. In this manner the soil adjacent the outer casing is kept in a moist, heat-conducting condition, and the transformer losses are dissipated both through the outer casing by conduction and by air currents. This construction is much more compact than the vaults heretofore used, and the double-walled unit is, of course, movable in its entirety from one location to another.

It is accordingly an object of my invention to provide a novel underground transformer unit which shall occupy less space than the vaults heretofore used in the art.

Another object of my invention is to provide a novel transformer unit which may be burieddirectly in the ground and which shall be provided with suitable means for preventing baking of the adjacent soil.

Another object of my invention is to provide a novel air cooled transformer unit suitable for 5 radial and network type underground distribution systems.

Other objects of my invention will become evident from the following detailed description taken in conjunction with the accompanying 10 drawing, in which:

Figure 1 is a sectional view partly in elevation and with parts broken away, showing an embodiment of my invention; and

Fig. 2 is a sectional view taken along the line 15 II-H of Fig. 1.

Referring to Fig. 1 in detail, an oil-filled distribution transformer I having cooling tubes 2 is rigidly secured within a casing 3 of good heat-conducting material, such as sheet steel, 20 by means of suitable steel supporting members 4,

5 and 6, in such a manner that air may be circulated freely around the cooling tubes 2. The members 4, 5 and 6, in addition to supporting the transformer I, also serve to conduct heat there- 25 from to the casing 3.

If the transformer I is provided with auxilia y switchgear apparatus, such apparatus may be mounted in the casing 3 with the transformer. In the arrangement shown, a network protector I 30 and a high voltage switch unit 8, are mounted within the casing 3, preferably at accessiblepositions on the transformer l as at the ends thereof, as shown.

The network protector 1 may be of the so- 3 called submersible type comprising a waterproof housing 'la within which are mounted a low voltage circuit breaker and suitable relay apparatus, of known type, for controlling the cir-. cuit breaker. As the construction of such net- 40 work protectors is well known in the art, detailed illustration and description thereof have, for simplicity, been omitted. The network protector 1 is provided with a handle 1b for operating the low voltage circuit breaker manually when such operation is necessary.

The switch unit 8 is also of waterproof construction, and has therein the usual high voltage disconnect and ground switch (not shown), submerged'under oil in a manner well understood in the art. The switch unit 8 is provided with a handle 8a for moving the disconnect and ground switch to open or closed position.

The sheet metal casing 3 is made water-proof in any suitable manner as by paint and composition coatings, so that it may be buried in the ground in the manner indicated in Fig. 1. Suitable means for draining the casing 3, which I have shown as a drain 9 and a crushed rock fill 10 below the drain, are provided for removing surface water which may accumulate in the casing. Obviously other well known drainage devices may v be used where desirable or necessary. In order to dissipate the heat losses of the transformer l and its auxiliaries without causing the soil around the casing 3 to become dry and baked, I provide means for circulating air from above the surface of the ground, around the transformer and associated apparatus and thence out above ground. To this end the casing 3 is provided with suitable ventilating openings l I which are fitted with manhole covers l2 and I3 of screened or grated construction. A vertical baiile it is provided below the manhole cover l2 to divide the space in the part of the casing 3 at the left in Fig. 1 into suitable air passages for maintaining convection currents about the network protector i and the left portion of the transformer l. The baiile It is'provided with suitable openings (not shown) for permitting free movement of the handle lb, and for permitting a set of low voltage cables 15 to be passed from the left end of the casing to suitable terminals of the network protector i. A fan I6 is provided for facilitating the circulation of air around the transformer I. The fan It is preferably mounted on the right wall-of the casing 3 within a sheet metal tube H in such a manner that a blast of air may be forced downward through the tube I1 and upward around the transformer l and associated apparatus.

The low voltage cables I5, mentioned above, are secured by means of a set of watertight glands IB in the left wall of. the casing. The high voltage windings of thetransformer are connected in any suitable manner through the switch unit 8 to the conductors of a high voltage cable l9.

In the construction shown, the conductors of the cable l9 are connected to insulating bushings 20, secured in the right wall of the casing 3. A pothead 2| is secured to the casing 3 around the external connections of the bushings 20, and is joined to the sheath of the cable If! by means of a wiped joint Mia. The pothead 2| is provided with a watertight plate 2M, through which connections may be made, and with a removable threaded plug 21b, which may be removed to fill .the pothead with insulating compound in-the usual manner. Suitable connectors 22 are provided for connecting the internal terminals of the bushings 20 to terminals of the switch unit 8. In place of the pothead construction described above, the high voltage cable l9 may be led through the right wall of the casing 3 to the switch unit 8, in the same manner as the low voltage cables l5.

The operation of the apparatus described above may be set forth as follows: Assuming the transformer l to be in operation, the heat losses of the transformer I and auxiliaries I and 8 are carried away partly by air currents produced by the fan l6 and by convection, and partly by conduction and radiation from the casing 8. The temperature of the casing 3 remains at a sufliciently low value to prevent drying of the adjacent soil, and to thereby insure free conduction of heat by the moist earth surrounding the easing. As part only of transformer losses are distails, arrangement of parts or circuit connections herein set forth as various modifications thereof may be effected without departing from the spirit and scope of my invention. I desire therefore that only such limitations shall be imposed as are indicated in the appended claims.

I claim as my invention: 5

1. A portable underground transformer unit comprising a metal outer casing having openings therein communicating with the atmosphere, a metal inner casing enclosed by said outer casin and spaced therefrom to provide passages for the 10 free circulation of air from said openings about said inner casing, transformer apparatus secured in said inner casing, a liquid cooling medium in said inner casing, and supporting means rigidly securing said inner casing to said outer casing 15 whereby said unit may be transported bodily and buried in the soil, said openings providing a thermal path for the dissipation of transformer losses additional to the path provided by conduction from said outercasing to the soil. 20

2. A portable underground transformer unit comprising a metal outer casing having openings therein communicating with the atmosphere, a metal inner casing enclosed by said outer casing and spaced therefrom to provide passages for 25 the free circulation of air from said openings about said inner casing, transformer apparatus secured in said inner casing, a liquid cooling medium in said inner casing, switch apparatus associated with said transformer apparatus, and sup- 30 porting means rigidly securing said inner casing, said outer casing and said switch apparatus to form a unitary structure, whereby said unit may be transported bodily and buried in the soil, said openings providing a thermal path for the dissipation of transformer losses additional to the path provided by conduction from said outer casing to the soil.

3. A portable underground transformer unit comprising a metal outer casing having a vented 40 manhole opening therein communicating with the atmosphere, a metal inner casing enclosed by said outer casing and spaced therefrom to provide passages for the free circulation of air from said manhole opening about said inner casing, trans- 45 former apparatus secured in said inner casing, a liquid cooling medium in said inner casing, and supporting means rigidly securing said inner cas- I ing to said outer casing whereby said unit may be transported bodily and buried in the soil, said 50 manhole opening providing a thermal path for the dissipation of transformer losses additional to the path provided by conduction from said outer casing to the soil.

4. A portable underground transformer unit 55 comprising a metal outer casing having openings therein communicating with the atmosphere and having a drainage opening near the bottom thereof, a metal inner casing enclosed by said outer casing and spaced therefrom to provide passages 69 for the free circulation of air from said openings about said inner casing, transformer apparatus secured in said inner casing, a liquid cooling medium in said inner casing, and supporting means rigidly securing said inner casing to said outer 65 casing whereby said unitmay be transported bodily and buried in the soil, said openings pro- ,viding a thermal path for the dissipation of 

